GENES VERSUS ENVIRONMENT - THE RELATIONSHIP BETWEEN DIETARY-FAT AND TOTAL AND CENTRAL ABDOMINAL FAT

OBJECTIVE - The influence of diet on body fat has not been quantified independently of genetic influences, although both are held to contrib ute to regulation of body fat stores. This study examined 1) the relat ionship between recent diet and total body and central abdominal fat i n middle-aged female twins independent of genetic and important enviro nmental factors and 2) evidence of interaction between diet and geneti c predisposition. RESEARCH DESIGN AND METHODS - Measurements in 436 he althy female twins (aged 58 +/- 10 years) included dietary intake by f ood frequency questionnaire (validated against a 7-day food diary, n = 162), BMI, total body and central abdominal fat by dual-energy X-ray absorptiometry, and environmental covariates (smoking habit, hormone r eplacement, and physical activity) by standardized questionnaire. Diet ary energy underreporters were excluded. RESULTS - Intake of dietary f at (total and subtype) and carbohydrates was not related to BMI or to total or central fat, confirmed in quintile analysis. With generic and environmental factors controlled in 90 monozygotic pairs, differences in the intake of energy, fat, or protein were not related to intrapai r differences in total and central body fat. However, a minor inverse relationship between carbohydrate intake and total adiposity was confi rmed (r = -0.25, P = 0.02). In paired analyses, the twin with the high er intake of total sugars had significantly lower total body and centr al abdominal adiposity. There was no evidence of a gene-environment in teraction between intake of fat or carbohydrates contributing to great er body fat mass in subjects genetically predisposed to obesity. CONCL USIONS - Using validated dietary measures and direct measures of body fat and excluding underreporters, no relationship between dietary fat and body fat was found in middle-aged women, particularly after contro lling for genetic and some environmental factors. The role of dietary factors in determining total body and central abdominal fat appears to have been overestimated in past cross-sectional studies.